A flip chip bonded structure for achieving size reduction and high-density mounting of semiconductor device has been receiving attention. The flip chip bonded structure has a structure wherein a semiconductor chip is connected to a solid device as directing its functional surface to the solid device, the functional surface being formed with a functional element.
FIG. 7 is an illustrative sectional view showing a structure of a conventional semiconductor device having the flip chip bonded structure. The semiconductor device 51 includes: a wiring board 52 having a connection surface 52a; and a semiconductor chip 53 having a functional surface 53a formed with a functional element and connected to the connection surface 52a as directing its functional surface 53a to the connection surface 52a. 
The connection surface 52a of the wiring board 52 is formed with a connection pad 58, which is formed of copper (Cu).
An electrode pad 54 connected with the functional element is formed on the functional surface 53a of the semiconductor chip 53. The functional surface 53a is covered with a surface protection film 55, which is formed with an aperture 55 to expose the electrode pad 54. An anti-diffusion film 56 is formed over the aperture 55a in a manner to cover an exposed surface of the electrode pad 54, the surface being exposed through the aperture 55a. As shown in FIG. 7, the anti-diffusion film 56 has a smaller thickness than that of the surface protection film 55, so that the anti-diffusion film 56 does not substantially project from the surfaces of the electrode pad 54 and the anti-diffusion film 56.
A ball-like connecting member 57 formed of a tin(Sb)-lead(Pb) solder material is interposed between the connection pad 58 of the wiring board 52 and the anti-diffusion film 56 of the semiconductor chip 53. Because of the connecting member 57 so interposed, the semiconductor chip 53 is supported as maintaining a predetermined distance from the wiring board 52, while electrical connection between the wiring board 52 and the semiconductor chip 53 is established.
On this account, the connecting member 57 normally has a far greater thickness than those of the connection pad 58 and the anti-diffusion film 56 with respect to a direction in which the wiring board 52 and the semiconductor chip 53 oppose each other.
Non-patent Document 1: J. D. Wu et al., “Electromigration Reliability of SnAgxCux Flip Chip Interconnects”, 54th Electron, Components and Technol. Conf., 2004, p. 961.